Light emitting diode

ABSTRACT

AC LED according to the present invention comprises a substrate, and at least one serial array having a plurality of light emitting cells connected in series on the substrate. Each of the light emitting cells comprises a lower semiconductor layer consisting of a first conductive compound semiconductor layer formed on top of the substrate, an upper semiconductor layer consisting of a second conductive compound semiconductor layer formed on top of the lower semiconductor layer, an active layer interposed between the lower and upper semiconductor layers, a lower electrode formed on the lower semiconductor layer exposed at a first corner of the substrate, an upper electrode layer formed on the upper semiconductor layer, and an upper electrode pad formed on the upper electrode layer exposed at a second corner of the substrate. The upper electrode pad and the lower electrode are respectively disposed at the corners diagonally opposite to each other, and the respective light emitting cells are arranged so that the upper electrode pad and the lower electrode of one of the light emitting cells are symmetric with is respect to those of adjacent another of the light emitting cells.

CROSS-REFERENCE RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/050,873, filed on Mar. 18, 2008, and claims priority from and thebenefit of Korean Application No. 10-2007-0026697, filed on Mar. 19,2007, which are hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND

1. Field

The present invention relates to a light emitting diode, and moreparticularly, to a light emitting diode, wherein a region of the lightemitting diode occupied by an upper electrode pad and a lower electrodeis designed to be small to thereby reduce a region where light emittedfrom the light emitting diode is blocked by the upper electrode pad andthe lower electrode and secure a larger light emitting area, therebyimproving light emission efficiency.

2. Background of the Invention

GaN-based light emitting diodes (LEDs) have been employed and developedfor about 10 years or more. The GaN-based LEDs considerably have changedLED technologies and are currently used for various applications, suchas full-color LED display devices, LED traffic lights and white LEDs.Recently, it has been expected that high-efficiency white LEDs willsubstitute for fluorescent lamps. Particularly, the efficiency of thewhite LEDs has reached the level similar to that of typical fluorescentlamps.

In general, an LED emits light by forward current and requires thesupply of DC. Hence, if the LED is connected directly to an AC powersource, it is repeatedly turned on/off depending on the direction ofcurrent. As a result, there are problems in that the LED does notcontinuously emit light and is easily broken by reverse current.

To solve such a problem, an LED capable of being connected directly to ahigh-voltage AC power source is disclosed in PCT Patent Publication No.WO 2004/023568(A1), entitled “LIGHT-EMITTING DEVICE HAVINGLIGHT-EMITTING ELEMENTS” by SAKAI et al.

According to PCT Patent Publication No. WO 2004/023568(A1), LEDs (i.e.,light emitting cells) are two-dimensionally connected in series on asingle insulative substrate such as a sapphire substrate to form LEDarrays. Such two LED arrays are connected to each other in reverseparallel on the sapphire substrate.

A GaN-based LED is generally formed by growing epitaxial layers on asubstrate such as sapphire and comprises an N-type semiconductor layer,a P-type semiconductor layer and an active layer interposedtherebetween. Meanwhile, an N-type electrode is formed on the N-typesemiconductor layer, and a P-type electrode is formed on the P-typesemiconductor layer. The LED is electrically connected to an externalpower source through the electrodes, thereby being driven. At this time,a current flows from the P-type electrode into the N-type electrode viathe semiconductor layers.

Since the P-type semiconductor layer generally has high specificresistivity, there is a problem in that the current cannot be uniformlydistributed but is concentrated on a portion at which the P-typeelectrode is formed. The current concentration leads to the reduction ofa light emitting area, and therefore, the light emission efficiency islowered. In order to solve such a problem, the technology fordistributing current by forming a transparent electrode layer with a lowspecific resistivity on a P-type semiconductor layer is used. Since thecurrent introduced from the P-type electrode is distributed in thetransparent electrode layer and flows into the P-type semiconductorlayer, the light emitting area of the LED can be expanded.

However, since the transparent electrode layer absorbs light, thethickness of the transparent electrode is restricted, and therefore,there is a limit in the current distribution. Particularly, alarge-sized LED having an area of about 1 mm² or more used for highpower has a limit in the current distribution using the transparentelectrode layer.

Meanwhile, the current flows through semiconductor layers and exitsthrough the N-type electrode. Thus, the current is concentrated on aportion of the N-type semiconductor layer on which the N-type electrodeis formed, which means that the current flowing in the semiconductorlayers is concentrated near the portion on which the N-type electrode isformed. Therefore, it is required to develop an LED capable of improvingcurrent concentration in an N-type semiconductor layer.

In the meantime, P-type and N-type electrodes formed in an LED generallyblock light emitted from the LED. Therefore, it is necessary to improvethe structure of the P-type and N-type electrodes, which can enhance thelight emission efficiency of the LED.

An object of the present invention is to provide an AC LED having anelectrode structure in which a current flowing in operation of the LEDcan be uniformly distributed and the light efficiency can be enhanced.

According to an aspect of the present invention for achieving theobjects, there is provided an AC LED, which comprises a substrate, andat least one serial array having a plurality of light emitting cellsconnected in series on the substrate. Each of the light emitting cellscomprises a lower semiconductor layer consisting of a first conductivecompound semiconductor layer formed on top of the substrate, an uppersemiconductor layer consisting of a second conductive compoundsemiconductor layer formed on top of the lower semiconductor layer, anactive layer interposed between the lower and upper semiconductorlayers, a lower electrode formed on the lower semiconductor layerexposed at a first corner of the substrate, an upper electrode layerformed on the upper semiconductor layer, and an upper electrode padformed on the upper electrode layer exposed at a second corner of thesubstrate. The upper electrode pad and the lower electrode arerespectively disposed at the corners diagonally opposite to each other;and the respective light emitting cells are arranged so that the upperelectrode pad and the lower electrode of one of the light emitting cellsare symmetric with respect to those of adjacent another of the lightemitting cells.

The serial array may comprise two serial arrays connected in reverseparallel to each other.

The two serial arrays connected in reverse parallel to each other, atleast one of the light emitting cells positioned in any one of theserial arrays is electrically connected to the corresponding one of thelight emitting cells positioned in the other serial array. Accordingly,it is possible to prevent overvoltage caused by a reverse voltage frombeing applied to a specific serial array during the operation of the ACLED.

The upper electrode layer may be a transparent electrode layer.

The transparent electrode layer may be formed of indium tin oxide (ITO)or Ni/Au.

The upper electrode pad may be formed of at least one selected from Ni,Cr, Pd, Pt, W and Al.

The upper electrode pad may comprise at least one layer or alloy layer.

The lower electrode may be formed of at least one selected from Ni, Cr,Pd, Pt, W and Al.

The lower electrode may comprise at least one layer or alloy layer.

The active layer may include a single quantum well or multiple quantumwell structure having an In_(x)Ga_(1-x)N (0<x<1) well layer and anIn_(x)Ga_(1-x)N (0≦x<1) barrier layer.

The In_(x)Ga_(1-x)N (0<x<1) well layer may have more In content than theIn_(x)Ga_(1-x)N (0≦x<1) barrier layer.

The second conductive compound semiconductor layer may includeAl_(x)Ga_(1-x)N (0≦x<1).

According to another aspect of the present invention, there is providedan AC LED, which comprises: two or more single chips electricallyconnected in series. Each of the single chips comprises a substrate, andat least one serial array having a plurality of light emitting cellsconnected in series on the substrate. Each of the light emitting cellscomprises a lower semiconductor layer consisting of a first conductivecompound semiconductor layer formed on top of the substrate, an uppersemiconductor layer consisting of a second conductive compoundsemiconductor layer formed on top of the lower semiconductor layer, anactive layer interposed between the lower and upper semiconductorlayers, a lower electrode formed on the lower semiconductor layerexposed at a first corner of the substrate, an upper electrode layerformed on the upper semiconductor layer, and an upper electrode padformed on the upper electrode layer exposed at a second corner of thesubstrate. The upper electrode pad and the lower electrode arerespectively disposed at the corners diagonally opposite to each other;and the respective light emitting cells are arranged so that the upperelectrode pad and the lower electrode of one of the light emitting cellsare symmetric with respect to those of adjacent another of the lightemitting cells.

The serial array may comprise two serial arrays connected in reverseparallel to each other.

The two or more single chips may be mounted on respective packages andare connected in series by a bonding wire.

The two or more single chips may be mounted on respective packages, andthe packages are connected in series.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating an LED having a single light emittingcell with an electrode structure according to one embodiment of thepresent invention;

FIG. 2 is a sectional view taken along line A-A of FIG. 1;

FIG. 3 is a schematic view illustrating an LED having a serial array ofthe light emitting cells shown in FIG. 1 according to embodiments of thepresent invention;

FIG. 4 is a partial sectional view illustrating light emitting cellsused in embodiments of the present invention;

FIG. 5 is a schematic view illustrating serial arrays of light emittingcells according to other embodiments of the present invention;

FIG. 6 is a photograph showing an electrode structure of an LEDaccording to one embodiment of the present invention;

FIG. 7 is a photograph showing an electrode structure of an LEDaccording to a comparative example to be compared with the electrodestructure of the LED according to the embodiment of the presentinvention;

FIG. 8 is a graph showing the light emission efficiency of the LEDaccording to the embodiment of the present invention; and

FIG. 9 is a graph showing the light emission efficiency of the LEDaccording to the comparative example.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Thefollowing embodiments are provided only for illustrative purposes sothat those skilled in the art can fully understand the spirit of thepresent invention. Therefore, the present invention is not limited tothe following embodiments but may be implemented in other forms. In thedrawings, the widths, lengths, thicknesses and the like of elements maybe exaggerated for convenience of illustration. Like reference numeralsindicate like elements throughout the specification and drawings.

FIG. 1 is a plan view illustrating an LED having a single light emittingcell with an electrode structure according to one embodiment of thepresent invention, and FIG. 2 is a sectional view taken along line A-Aof FIG. 1. The technical structures and characteristics, which are usedin describing the LED having a single light emitting cell with anelectrode structure according to the embodiment of the present inventionillustrated in FIGS. 1 and 2, will be adaptively used in the followingvarious embodiments related to FIGS. 3 to 9 so long as there is noadditional description.

Referring to FIGS. 1 and 2, the LED 1 a having a single light emittingcell with an electrode structure according to the embodiment of thepresent invention has a first conductive lower semiconductor layer 55,an active layer 57 and a second conductive upper semiconductor layer 59,which are formed on a substrate 51. In the following drawings, the LED 1a will be adaptively shown as a light emitting cell 1 without departingfrom the fundamental spirit of the invention.

The active layer 57 may have a single or multiple quantum well structureincluding a well layer and a barrier layer, and the substance andcomposition thereof is selected depending on a required light emissionwavelength. For example, the active layer 57 may be formed of aGaN-based compound semiconductor. Alternatively, the active layer 57 mayhave, for example, an In_(x)Ga_(1-x)N (0<x<1) well layer and anIn_(x)Ga_(1-x)N (0≦x<1) barrier layer. The In_(x)Ga_(1-x)N(0<x<1) welllayer may be formed to have more In content than the In_(x)Ga_(1-x)N(0≦x<1) barrier layer.

In the meantime, the lower and upper semiconductor layers 55 and 59 areformed of a material with a greater band gap than the active layer 57and may be formed of a GaN-based compound semiconductor. For example, asecond conductive compound semiconductor layer constituting the lowersemiconductor layer 55 may include Al_(x)Ga_(1-x)N (0≦x<1).

Meanwhile, a buffer layer 53 may be interposed between the lowersemiconductor layer 55 and the substrate 51. The buffer layer 53 isemployed to reduce mismatch between the substrate 51 and the lowersemiconductor layer 55.

As shown in FIG. 2, the upper semiconductor layer 59 is positioned on apartial region of the lower semiconductor layer 55, and the active layer57 is interposed between the upper and lower semiconductor layers 59 and55. In addition, an upper electrode layer 61 may be positioned on theupper semiconductor layer 59. The upper electrode layer 61 that is atransparent electrode layer may be formed, for example, of a materialsuch as indium tin oxide (ITO) or Ni/Au.

Meanwhile, a lower electrode 65 is positioned on the lower semiconductorlayer 55 exposed at a first corner (a bottom left corner of FIG. 1) ofthe substrate 51. The upper electrode layer 61 is formed on the uppersemiconductor layer 59, and an upper electrode pad 64 is positioned onthe upper electrode layer 61 at a second corner (a top right corner ofFIG. 1) of the substrate 51. The upper electrode pad 64 may be formed ofat least one selected from Ni, Cr, Pd, Pt, W and Al using a lift-offtechnique. The upper electrode pad 64 may include at least one layer oralloy layer.

When the lower semiconductor layer 55 is of an N type, the lowerelectrode 65 may be formed of Ti/Al using a lift-off technique. Besides,the lower electrode 65 may be formed of at least one selected from Ni,Cr, Pd, Pt, W and Al, and may include at least one layer or alloy layer.

The upper electrode layer 61 that is a transparent electrode layer isformed, for example, of ITO or Ni/Au to have transparency and is inohmic contact with the upper semiconductor layer 59 to lower contactresistance. However, the upper electrode pad 64 does not havetransparency and is not in ohmic contact with the upper semiconductorlayer 59. As the upper electrode layer 61 is formed between the upperelectrode pad 64 and the upper semiconductor layer 59, it is possible toprevent current from being concentrated under the upper electrode pad 64and to prevent light from being absorbed and lost by the upper electrodepad 64.

In addition, the upper electrode pad 64 with a relatively small area isformed at a corner of the upper semiconductor layer 59, therebyimproving current distribution in the upper semiconductor layer 59.

Moreover, the upper electrode pad 64 and the lower electrode 65 aredisposed at corners of the substrate 51 opposite to each other,respectively. Accordingly, the current supplied through the upperelectrode pad 64 can be uniformly distributed in the upper electrodelayer 61.

FIG. 3 is a schematic view illustrating an LED having a serial array ofthe light emitting cells shown in FIG. 1 according to embodiments of thepresent invention. The serial array is disposed in a single chip 50.

Referring to FIG. 3, the single chip 50 has a substrate 51. Thesubstrate 51 may be insulative substrate or a conductive substratehaving an insulating layer formed on a top surface thereof. A pluralityof light emitting cells 1 are disposed on the substrate 51. The lightemitting cells are connected in series to one another by wires to form aserial array 52. Bonding pads 71 may be positioned at both ends of theserial array 52. The bonding pads 71 are electrically connected to boththe ends of the serial array 52, respectively.

In the embodiments of the present invention, the light emitting cells inthe single chip 50 may be all connected in series on the singlesubstrate. Thus, the processes of forming the light emitting cells 1 ona single substrate and forming wires for connecting the light emittingcells 1 are simplified.

FIG. 4 is a partial sectional view illustrating light emitting cellsused in embodiments of the present invention, in which the lightemitting cells are connected in series through wires formed by a stepcover process. However, the light emitting cells may be connected inseries through wires formed by an air bridge process as well as the stepcover process. Referring to FIG. 3, a plurality of the light emittingcells 1 are spaced apart from one another on a substrate 51. Each of thelight emitting cells 1 comprises a lower semiconductor layer 55consisting of a first conductive compound semiconductor layer, an activelayer 57 and an upper semiconductor layer 59 consisting of a secondconductive compound semiconductor layer. The active layer 57 may have asingle or multiple quantum well structure including a well layer and abarrier layer, wherein the substance and composition of the active layer57 is selected depending on a required light emission wavelength. Forexample, the active layer 57 may be formed of a GaN-based compoundsemiconductor. The lower and upper semiconductor layers 55 and 59 may beformed of a material with a greater band gap than the active layer 57and formed of a GaN-based compound semiconductor.

Meanwhile, a buffer layer 53 may be interposed between the lowersemiconductor layer 55 and the substrate 51. The buffer layer 53 isemployed to reduce mismatch between the substrate 51 and the lowersemiconductor layer 55. As shown in the figure, the buffer layer 53 maybe formed to have portions spaced apart from each other, but the presentinvention is not limited thereto. If the buffer layer 53 is formed of aninsulative material or a material with large resistance, the bufferlayer 53 may be formed continuously over the substrate 51.

As shown in this figure, the upper semiconductor layer 59 is positionedon a partial region of the lower semiconductor layer 55, and the activelayer 57 is interposed between the upper and lower semiconductor layers59 and 55. In addition, an upper electrode layer 61 may be positioned onthe upper semiconductor layer 59. The upper electrode layer 61 that is atransparent electrode layer may be formed, for example, of a materialsuch as indium tin oxide (ITO) or Ni/Au.

Meanwhile, the light emitting cells 1 are electrically connected throughwires 87. The lower semiconductor layer 55 of one of the light emittingcells is connected to the upper electrode layer 61 of adjacent anotherof the light emitting cells by the wire 87. As shown in this figure,upper electrode pads 64 formed on the upper electrode layer 61 may beconnected to lower electrodes 65 formed on exposed regions of the lowersemiconductor layer 55 through the wires 87, respectively.

The wires 87 for connecting the light emitting cells 1 may be formed bya step cover process. That is, all the layers of the light emittingcells 1 and the substrate 51 are covered with an insulating layer 85,except portions for contacting the wires 87. Then, the wires 87 arepatterned on the insulating layer 85, so that the light emitting cells 1are electrically connected to one another.

For example, the insulating layer 85 has openings for exposing the upperelectrode pads 64 and the lower electrodes 65. The wires 87 connect theupper electrode pads 64 and the lower electrodes 65 of the lightemitting cells adjacent to each other through the openings, whereby thelight emitting cells are connected in series. Thus, the serial array 52(see FIG. 3) is formed, in which the light emitting cells are connectedin series by the wires 87 on the single substrate 51.

As described above, an AC LED using a single chip having a serial arrayon a substrate has been described. However, an AC light emitting devicemay be configured using single chips, each of which has a serial array,connected in reverse parallel on a substrate.

FIG. 5 is a schematic view illustrating an AC LED using a single chip100 having serial arrays connected in reverse parallel on a singlesubstrate.

Referring to FIG. 5, two serial arrays 52 a and 52 c, each of which haslight emitting cells 1 connected in series, are disposed on a substrate51. The serial arrays 52 a and 52 c are connected in reverse parallel toeach other between bonding pads 71 a and 71 b.

When such single chips 100 are connected in series to each other by aconnecting means (not shown), at least two array groups may be formed.The connecting means may be a bonding wire for directly connectingbonding pads. That is, single chips are mounted on respective packages,and the single chips mounted on the respective packages are connected toone another by bonding wires, thereby forming several array groups.Alternatively, as described above, the single chips 100 are mounted onrespective packages, and the respective packages are connected inseries, thereby forming several array groups. Besides, serial arraygroups may be variously formed using single chips and packages.

Meanwhile, the corresponding light emitting cells 1 in the respectiveserial arrays 52 a and 52 c formed on the same substrate 51 areelectrically connected by connecting means 105. That is, in the twoserial arrays 52 a and 52 c connected in reverse parallel to each other,at least one light emitting cell positioned in any one of the serialarrays is electrically connected to at least one corresponding lightemitting cell positioned in the other of the serial arrays by theconnecting means 105. The connecting means 105 prevents overvoltage frombeing applied to light emitting cells in a serial array to which thereverse voltage is applied. The connecting means 105 may connect firstconductive lower semiconductor layers, each of which is commonly used byadjacent ones of the light emitting cells 1 in each of the serial arrays52 a and 52 c, to one another. Alternatively, the connecting means 105may connect wires formed to connect adjacent ones of the light emittingcells 1 in the respective serial arrays 52 a and 52 c to one another inseries.

According to this embodiment, several single chips 100, in each of whichthe serial arrays 52 a and 52 c each having light emitting cellsserially connected are connected in reverse parallel to one another, areconnected in series to form several array groups, thereby decreasing thenumber of light emitting cells in a serial array on a single substrate.

FIG. 6 is a photograph showing an electrode structure of an LEDaccording to one embodiment of the present invention.

Referring to FIG. 6, several light emitting cells are disposed in anarray on a substrate. The respective light emitting cells areelectrically connected to one another by connecting means by a stepcover process.

It can be seen that an upper electrode pad and a lower electrode, whichare provided in each light emitting cell, are respectively disposed atcorners opposite to each other. A percentage of the area occupied by theupper electrode pad and the lower electrode in each light emitting cellis relatively small. In addition, such a configuration in one of thelight emitting cells is disposed symmetrically with respect to adjacentanother of the light emitting cells. That is, the upper electrode padand the lower electrode in each light emitting cell are diagonallydisposed at corners, respectively. The upper electrode pad and the lowerelectrode of one of the light emitting cells are arranged to besymmetric with respect to those of adjacent another of the lightemitting cells.

As the upper electrode pad and the lower electrode provided in eachlight emitting cell are respectively disposed at corners opposite toeach other, the respective light emitting cells can be disposed so thatthe length of a connecting means is minimized when two of the lightemitting cells are electrically connected to each other.

For example, first, second and third light emitting cells 1, 2 and 3 arearranged in a line. At this time, the first light emitting cell 1 has alower electrode disposed a left bottom corner and an upper electrode paddisposed at a right top corner. Further, the second light emitting cell2 has a lower electrode disposed a left top corner and an upperelectrode pad disposed at a right bottom corner. Furthermore, the thirdlight emitting cell 3 has a lower electrode disposed a left bottomcorner and an upper electrode pad disposed at a right top corner.

Moreover, a fourth light emitting cell 4 has an upper electrode paddisposed at a left top corner and a lower electrode disposed at a rightbottom corner. The third and fourth light emitting cells 3 and 4 areconnected to each other by a connecting means.

As described above, the upper electrode pad and the lower electrode arerespectively disposed at corners opposite to each other in each lightemitting cell, thereby simplifying processes and enhancing reliabilitywhen fabricating an AC LED.

In addition, the upper electrode pad and the lower electroderespectively disposed at corners opposite to each other in each lightemitting cell are small in size, whereby an area, in which light emittedfrom the LED is blocked by the upper electrode pads and the lowerelectrodes, is small, and a light emitting area is large.

FIG. 7 is a photograph showing an electrode structure of an LEDaccording to a comparative example to be compared with the electrodestructure of the LED according to the embodiment of the presentinvention.

Referring to FIG. 7, an upper electrode pad and a lower electrode arerespectively formed to extend at edges of both opposite sides in eachlight emitting cell disposed in the LED according to the comparativeexample. It can be seen that a percentage of the area occupied by theupper electrode pad and the lower electrode in each light emitting cellis considerably larger than that of FIG. 6. Thus, it can be seen that asthe area occupied by an upper electrode pad, a lower electrode and awire is wide, the light emitting area is decreased.

FIG. 8 is a graph showing the light emission efficiency of the LEDaccording to the embodiment of the present invention, and FIG. 9 is agraph showing the light emission efficiency of the LED according to thecomparative example.

That is, FIG. 8 shows the optical power outputted from each lightemitting cell provided in the LED shown in FIG. 6 according to theembodiment of the present invention, in which the number of lightemitting cells for every optical power value is shown.

FIG. 9 shows the optical power outputted from each light emitting cellprovided in the LED shown in FIG. 7 according to the comparativeexample, in which the number of light emitting cells for every opticalpower value is shown. At this time, the light emitting cells shown inFIGS. 6 and 7 have the same size.

Referring to FIG. 8, the optical power of each light emitting cellprovided in the LED according to the embodiment of the present inventionis measured as 135 mW on the average. Referring to FIG. 9, the opticalpower of each light emitting cell provided in the LED according to thecomparative example is measured as 119 mW on the average.

Through the comparison results, it can be seen that the light emissionefficiency of the LED according to the embodiment of the presentinvention is superior to that of the LED according to the comparativeexample.

According to the present invention, a region occupied by an upperelectrode pad and a lower electrode is designed to be small, so that aregion in which light emitted from the LED is blocked by the upperelectrode pads and the lower electrodes is reduced and a light emittingarea is large, thereby improving the light emission efficiency.

Further, an upper electrode pad and a lower electrode in an LED arerespectively disposed at corners opposite to each other, therebymaximizing current distribution.

Furthermore, an upper electrode pad and a lower electrode of each lightemitting cell are respectively disposed at corners even when lightemitting cells are electrically connected in order to stably operate anAC LED. This, a connection circuit can be configured to have theshortest path between the upper electrode pad of one of the lightemitting cells and the lower electrode of adjacent another of the lightemitting cells, thereby simplifying a process of fabricating the AC LEDand enhancing reliability.

The present invention described above is not defined by theaforementioned embodiments, but various modifications and changes can bemade thereto by those skilled in the art and are included in the spiritand scope of the invention defined by the appended claims.

For example, various structures of serial arrays having seriallyconnected light emitting cells have been described in FIGS. 3 to 5.However, although not shown in the respective figures, each lightemitting cell 1 included in each serial array has an electrode structuredescribed in detail in connection with FIGS. 6 to 9. That is, an upperelectrode pad and a lower electrode, which are formed in each lightemitting cell 1, are respectively disposed at corners diagonallyopposite to each other, and the respective light emitting cells 1 arearranged so that the upper electrode pad and the lower electrode in oneof the light emitting cells are symmetric with respect to those inadjacent another of the light emitting cells. The advantages of such anelectrode structure have been fully described in connection with FIGS. 6to 9.

What is claimed is:
 1. A light emitting diode, comprising: a substrate;a first array including a first light emitting cell, a second lightemitting cell and a third light emitting cell, the first array includinga first portion and a second portion; a first connector seriallyconnecting the first light emitting cell and the second light emittingcell; and a second connector serially connecting the second lightemitting cell and the third light emitting cell, wherein the first, thesecond and the third light emitting cells are disposed along animaginary line and the imaginary line is disposed between the first andthe second portions, and wherein the first and second connectors aredisposed on the first portion and second portion of the first array,respectively.